The relative amounts of vector DNA to carrier were 1.2 μl of in vivo-jetPEI per 10 μg of DNA at N/P = 6. The DNA–polymer complexes or in vivo-jetPEI alone were diluted with 5% dextrose in water to a total volume of 20 μl and allowed to stand for 15 min at room temperature before use. After incubation, 3 μl of in vivo-jetPEI/DNA polyplexes were used for spinal nerve injection and intra-DRG injection, and 10 μl of in vivo-jetPEI/DNA polyplexes were used for intrathecal injection.

Delivering gene constructs into the dorsal root ganglia (DRG) is a powerful but challenging therapeutic strategy for sensory disorders affecting the DRG and their peripheral processes. The current delivery methods of direct intra-DRG injection and intrathecal injection have several disadvantages, including potential injury to DRG neurons and low transfection efficiency, respectively. This study aimed to develop a spinal nerve injection strategy to deliver polyethylenimine mixed with plasmid (PEI/DNA polyplexes) containing green fluorescent protein (GFP). Using this spinal nerve injection approach, PEI/DNA polyplexes were delivered to DRG neurons without nerve injury. Within one week of the delivery, GFP expression was detected in 82.8% +/- 1.70% of DRG neurons, comparable to the levels obtained by intra-DRG injection (81.3% +/- 5.1%, p = 0.82) but much higher than those obtained by intrathecal injection. The degree of GFP expression by neurofilament(+) and peripherin(+) DRG neurons was similar. The safety of this approach was documented by the absence of injury marker expression, including activation transcription factor 3 and ionized calcium binding adaptor molecule 1 for neurons and glia, respectively, as well as the absence of behavioral changes. These results demonstrated the efficacy and safety of delivering PEI/DNA polyplexes to DRG neurons via spinal nerve injection.